The present disclosure generally relates to photocatalysts and, more particularly, to semiconducting photocatalysts having visible light activity.
Photocatalysts have garnered significant attention not only for their potential use in the production of hydrogen and/or oxygen from water, but also in the treatment of waste materials and purification of air. Photocatalysts are frequently formed from semiconductors or from organometallic complexes, such as chlorophyll. Of the two, semiconductors are generally preferred owing in part to their chemical stability, low cost of production, broad energy bandgaps, and the ease with which they can be handled.
Semiconductor photocatalysis is initiated by the direct absorption of a photon, which creates separated electrons and holes across the energy bandgap. The strongly reducing electrons and the strongly oxidizing holes, generated by the optical excitation, must move to the surface of the semiconductor in order to be used in the particular catalytic cycle.
Photocatalytic processes that make use of solar energy are highly desirable. The intensity of sunlight is strongest at a wavelength of about 500 nanometers (nm), and the overall visible light region accounts for about 43% of solar energy. Thus, to effectively utilize solar energy, it would be advantageous for the photocatalyst to be sensitive to visible light. Unfortunately, early semiconductor photocatalysts exhibited limited or zero visible light activity and instead were sensitive to ultraviolet (UV) light, which only accounts for about 5% of sunlight.
Although more recently developed photocatalysts have improved visible light activity, they suffer from poor efficiency and/or stability, such as when they undergo photocorrosion (i.e., when holes in the valence band react with the photocatalyst itself, resulting in decomposition). There accordingly remains a need in the art for new and improved photocatalysts.